Photographic paper treated with electron bombarded chromic complexes



United States Patent 3 117,865 PHQTOGRAPHIC PAPZER TREATED WITH ELEC- TRON BOR'IBARDED HROMHZ CGMPLEXES Irvin H. Crawford and William J. Venor, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed May 4, 1961, Ser. No. 107,636 5 Claims. (Cl. 9685) This invention concerns water-resistant photographic paper, more particularly photographic paper resistant to moisture penetration.

Photographic paper is customarily made of paper pulp of high purity which is sized with an internal size selected for its compatibility with photographic emulsions and in order to obtain certain properties such as stiffness, hardness, and the like. Subsequently, the paper is then normally coated with a layer of barium sulfate in a gelatin binder to provide a white surface of high reflectance and then overcoated with a light-sensitive silver halide emulsion. This paper is subject to moisture penetration and it changes in dimensional stability. However, there has been an increasing demand in the photographic industry for photographic paper which is dimensionally stable to humidity changes and to immersion in water. Many of the materials which might be used are hydrophobic so that there is a problem of adhering a photographic emulsion to the surface. Others are expensive, difiicult to apply on a paper substrate, or incompatible with photographic emulsions. We have found a method of preparing a water-resistant substrate which is compatible with photographic emulsions, and which has good adhesion to the emulsions.

One object of this invention is to provide photographic paper which is dimensionally stable to humidity changes and to immersion in water. Another object is to provide a process of treating photographic paper to reduce the moisture penetration of the paper and at the same time to obtain good adhesion to photographic emulsions. An additional object is to provide a method of treating paper having thereon a chromium complex to obtain good adhesion to subsequent coatings.

The above objects are obtained by dip coating or tub sizing photographic paper with a chromium halide com plex of a long chain fatty acid of 14-18 carbon atoms such as stearato chromic chloride, or the like, in an amount of 1.52.0 g./ft. of solution to paper. This results in a dry basis of between 0.0150.04 g./ft. The amount of chromium halide complex solution which is absorbed by the paper depends on the stock weight of the paper, its finish, and the like. The proportions are relatively critical, since a limit lower than 1% will not impart desirable water repellency and an amount above about 4% may impart a green tint to the paper which is undesirable. After sizing with the chromium complex, the paper may be subjected to heating at a temperature of about 200280 F. and dried. The best treatment may be omitted but a longer drying period is required at room temperature. The paper may then be calendered.

After the paper has been sized preferably using a tub size method of applying the material, the surface of the paper is subjected to electron bombardment using the corona type electron bombardment.

In our preferred embodiment paper made from partially acetylated fiber (as described in US. patent application Serial No. 786,041 in the names of William H. Griggs et a1.) having a weight of 11 lbs./th. ft. was tub sized with the following solution:

Stearato chromic chloride (30%) Neutralizing solution (16.5% urea, 5.0% sodium formate, and 0.2% formic acid in water) 5 Water 275 While the paper is still moist, it is subjected to 220 F. heat supplied by radiant heaters and dried. The paper is calendered and electron bombarded by passing through electron bombardment apparatus at a speed of 2 ft./min. under 9 electrodes at a voltage of about 50,000 volts, and a frequency of 4-5 megacycles.

The paper is then sensitized with an unwashed, finegrain silver chloride photographic emulsion.

Various chromium complexes can be used in our process including the following structural formulas:

EXAMPLE 1 A series of coatings were made on paper stock having a weight of 10 lbs./ 1000 ft? using each of the three typical chromium complexes identified as A, B, and C above. Two percent solutions were prepared resulting in a dry coating of 30-40 g./ 1000 ft. Each of the coatings was preheated at a temperature of 220 F. using radiant type heaters, calendered, and electron bombarded by passing under a corona discharge under the conditions disclosed above as our preferred embodiment. An unsized sample was also similarly treated. The following table shows the resistance to water penetration as determined using the standard tests of Valley penetration and Cobb size.

Patented Jan. 14, 1964 I Partially acetylated paper having a weight of lbs. per 1000 square feet was sized with the following composi- 'tion:

Percent by wt.

Polyvinyl acetate (55% solids) 20.8 Stearato chrornic chloride solids) 16.7 Di-butylphthalate 1.1 Water 61.4

Excellent adhesion resulted when an unwashed, finegrained silver chloride photographic emulsion was coated on the dried paper.

Chromium halide complexes can be applied in a mixture of alcohol and water. The alcohol is not necessary in carrying out our invention but aids in the penetration of the chrome complex into the paper Web.

Various photographic emulsions can be coated on the paper prepared according to our invention. All of these silver halide emulsions have improved adhesion to the paper sized with the chromium halide complexes and then electron-bombarded.

The method of electron bombarding may be varied depending upon the type of equipment used. For instance, on a low-energy laboratory device, a pass of the paper at 2 feet per minute under 9 electrodes provides a satisfactory paper. However, a similar degree of adhesion is obtained when the same type of paper is passed at a speed of 150 feet per minute using 6 electrodes on a high-energy unit.

The method of determining the hydrophilic nature of the surface can be employed involving measuring the contact angle of a drop of water on the surface. A drop of distilled water is placed on a level sample, projecting the image of the drop and sample on a suitable screen and measuring the angle obtained by drawing a line tangent to the drop image at the point the edge of the drop touches the sample. This contact angle can be measured quickly and accurately by using a contour projector as the means of projection. Untreated chromium halide complex sized paper gives a contact angle of about 90. A minimum electron bombardment needed for emulsion adhesion gives a contact angle of about 73, although it will be appreciated that lower contact angles would also be operative and advantageous in adhering photographic emulsions to the sized paper support.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modificatons can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

in an amount of 0.0l50.04 gram per square foot and said chromium halide complex having been subjected to electron bombardment to obtain a contact angle of less than 74 measured with Water.

2. A photographic paper having thereon 0015-004 gram per square foot of a chromium halide complex selected from the class consisting of and ( C n aa and and

heating to a temperature of about 200280 F. until dry, electron bombarding to obtain a contact angle of less than 74 measured with Water, and coating With a silver halide photographic emulsion.

5. A photographic paper comprising a partially acetylated fiber paper base having thereon 0.0154104 gram per square foot of a chromium halide complex selected from the class consisting of and electron bombarding to obtain a contact angle of less than 74 measured with water, and having thereover a light sensitive silver halide emulsion.

References Cited in the file of this patent UNITED STATES PATENTS 2,910,378 'Hauserman Oct. 27, 1959 2,925,340 Bryce et a1 Feb. 16, 1960 2,989,633 Wilson e r r June 20, 1961 

2. A PHOTOGRAPHIC PAPER HAVING THEREON 0.015-0.04 GRAM PER SQUARE FOOT OF A CHROMIUM HALIDE COMPLEX SELECTED FROM THE CLASS CONSISTING OF 